Whenever a new map is released, that map becomes the background permanently for a week, then gets put into the rotation. Same with the case when a new hero is released, that hero also stand in the background permanently for a week.

New hero backgrounds

Starting with Doomfist, every new hero would have their own map background, available only in the first week of the hero's release. The maps these backgrounds used are slightly modified, or in a different area than normal.

Trivia

Some maps in the background are slightly different than they are in-game.

Hanamura has a small pavilion in the middle of the cherry blossom yard. On the menu, this is replaced by a slightly elevated stone platform.

Volskaya Industries has a catwalk in-game that is absent in the menu.

King's Row's attackers spawn room has two doors on either side of the front wall. On the menu, it is just one big door.

Patch Changes

March 21, 2017Patch:Fixed a bug causing Reaper's shotguns and D.Va's mech to appear unusually large on the main menu.

December 20, 2016Patch:Mouse 4 no longer controls backwards menu navigation, preventing conflicts with other functions that might be bound to that. Fixed a bug preventing audio from mixing correctly on the main menu screen button.